(19)

(11)

EP 2 171 499 A2

(12)

(43) Date of publication: 07.04.2010 Bulletin 2010/14 (21) Application number: 08782109.6 (22) Date of filing: 19.07.2008

(51) International Patent Classification (IPC):  G01V 1/00(2006.01) (86) International application number: PCT/US2008/070575 (87) International publication number: WO 2009/017993 (05.02.2009 Gazette 2009/06)

(84) Designated Contracting States: AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MT NL NO PL PT RO SE SI SK TR (30) Priority: 02.08.2007 US 833094 (71) Applicant: Chevron U.S.A., Inc. San Ramon, CA 94583 (US)	(72) Inventors: MAGILL, James R. Walnut Creek, California 94598 (US) WASHBOURNE, John K. Walnut Creek, California 94597 (US) (74) Representative: Nash, David Allan  Haseltine Lake LLP Redcliff Quay 120 Redcliff Street Bristol BS1 6HU Bristol BS1 6HU (GB)